1. Field of the Invention
This invention is directed to lighting fixtures that use solid-state electronic devices as the lighting elements.
2. Related Art
Conventionally, industrial, commercial and, occasionally, residential spaces are illuminated using fluorescent tubes or high-intensity-discharge (HID) lamps. High-intensity discharge (HID) lamps include these types: mercury vapor electrical lamps, metal halide (HQI) electrical lamps, high-pressure sodium (Son) electrical lamps, low-pressure sodium (Sox) electrical lamps and less common, xenon short-arc lamps. The light-producing element of these lamp types is a well-stabilized arc discharge contained within a refractory envelope (arc tube). Whichever metal is used, the lamp produces the light once the metal is heated to a point of evaporation, forming a plasma in the arc tube. Like fluorescent lamps, HID lamps require a ballast to start and maintain their arcs.
However, fluorescent tubes and HID lamps have minimal options for varying light output. Due to their modes of operation, it is difficult and expensive, if not impossible, to moderate the amount of light emitted by a fluorescent tube or an HID lamp. Likewise, due to aging effects and the like, completely turning off and on fluorescent tubes and HID lamps on a need-for-illumination basis is generally discouraged.